This invention relates generally to angle-to-current converters generating an electrical current output in direct proportion to the degree of angular displacement of an input shaft, and in particular to a converter which makes use of a differential-inductance transducer.
While the invention will be described as it operates in conjunction with a variable-area flowmeter to transmit a current signal which is a function of flow rate to a remote station, it is to be understood that the angle-to-current converter in accordance with the invention is usable in any situation wherein the angular displacement of a shaft must be transmitted in the form of a corresponding electrical signal.
In a flowmeter of the variable-area tube type, the fluid to be metered is conducted through the tube to cause a float movable vertically therein to assume a position of equilibrium between the downward force of the flow and the upward force of the fluid flowing past the float through the surrounding annular orifice.
In many flowmeter applications, it is necessary to translate the changing vertical position of the float within the flow tube into a corresponding external indication. Where, for example, the process fluid is opaque, the float cannot be seen through the transparent tube; hence direct visual indication along the tube is precluded. In other situations, the flow tube must be made of metal or other opaque material, so that it is then necessary to provide means for registering the float position at a point external to the tube.
It is known for this purpose to use a magnetic follower in which the float in the variable-area tube is provided with a guided extension rod to which a bar magnet is attached. The bar magnet moves up and down in accordance with changes in the vertical float position and is magnetically linked with a rotatable follower magnet mounted on a shaft to which an indicating pointer is attached. The follower magnet is caused to rotate in a direction and to an extent that is a function of the bar magnet movement and hence of flow rate.
In applicant's copending application entitled "Pneumatic Transmitter for Variable Area Flowmeter," now U.S. Pat. No. 4,019,369 there is disclosed an angle-to-pneumatic signal converter which is coupled to the magnetic follower associated with a variable area flowmeter and adapted to convert the rotation of the follower shaft which corresponds to the rise and fall of the float into a transmittable pneumatic signal whose value is proportional to flow rate.
The present invention deals with an electrical transmitter which carries out a similar function, except that in lieu of a pneumatic signal, a current signal is generated, making it possible to transmit this signal to a remote indicating or control station over a current-carrying line.